Oxidative hair dyeing process with dihydroxybenzenes and aminoethanethiols

ABSTRACT

A process of dyeing hair by preparing and applying to the hair an aqueous reaction medium comprising an aminoethanethiol, a dihydroxybenzene and a ferricyanide or persulfate oxidizing agent, the composition optionally containing a color modifier selected from the group consisting of direct dyes, primary intermediates, couplers and mixtures thereof, and also containing a buffer to maintain the pH in the range from 2 to 11 during the oxidation reaction, and removing the aqueous reaction medium from the hair after the desired color is attained, and compositions and kits for practicing such processes.

This application is a continuation-in-part of U.S. Ser. No. 08/174,488filed Dec. 27, 1993, now abandoned.

FIELD OF THE INVENTION

This invention relates to compositions, methods and kits for dyeinghair. More specifically, the invention relates to methods of dyeing hairin which mixtures of certain dihydroxybenzenes and aminoethanethiols areoxidized to produce phaeomelanin, phaeomelanin-like, trichochrome andtrichochrome-like pigments for coloring human hair. The inventionrelates also to compositions for conducting the hair dyeing process andto the packaged reactants sold in the form of a kit.

BACKGROUND OF THE INVENTION

Modern hair dyeing has developed from its initiation in the 1950's tothe point where, today, it is the third largest product type in the haircategory following shampoos and conditioners.

A wide variety of hair dyes or colorants have been developed, many ofwhich involve oxidation of selected organic compounds or combinations ofsuch compounds with oxidizing agents such as hydrogen peroxide. Otherknown oxidizing agents for use with such compounds include perborates,persulfates and perhalites, particularly periodates. These oxidizingagents are generally employed as ammonium salts or as salts of alkalimetals. In the course of this development, it has been learned that theapplicability of an oxidant to one or more oxidizable substrates doesnot permit the prediction that the same oxidant or apparently similaroxidant will be useful for oxidizing another oxidizable substate toachieve a desirable color change in human hair.

Despite the large number of hair dyeing compositions and processes whichhave been developed, the art is constantly searching for methods andcompositions to improve the efficiency of the hair coloring process,decrease the time required, impart desirable tints and tones to the hairand avoid and use of hydrogen peroxide, which may be damaging to hair orskin.

PRIOR ART

U.S. Pat. No. 4,746,322 to Herlihy describes hair coloring procedures inwhich hair is colored by oxidation of 3,4-dihydroxyphenylalanine (dopa)or its derivatives by an iodate or periodate oxidant (possibly inadmixture with a persulfate) and in the presence of selected dispersingagents.

BRIEF SUMMARY OF THE INVENTION

In the process of the present invention human hair is dyed to attaindesirable permanent tints and tones by applying to the hair selectedaminoethanethiols and selected dihydroxybenzenes together with anoxidizing agent selected from the group consisting of persulfates andferricyanides contained in one or more aqueous compositions. The hair isdyed at a pH of from about 2 to about 11, preferably from about 5 toabout 9. The dihydroxybenzenes employed in the invention are o- andp-dihydroxybenzenes, which may be further substituted as describedbelow.

Among the important advantages achieved by the practice of thisinvention is that the oxidative development of color is accomplishedwithout the use of hydrogen peroxide, thereby avoiding the knowndisadvantages of this oxidizing agent. Another advantage is that atleast some of the end products of the oxidation reaction are expected tobe identical to or closely related to trichochromes or phaeomelanins,which are the natural red and yellow pigments present in hair. Thus, bythe practice of this invention it is possible to achieve natural lookingred and yellow hair tones that have heretofore eluded the art.

The reactants employed in this invention are all well known or can beproduced by well known procedures.

DETAILED DESCRIPTION OF THE INVENTION

The hair dyeing process of the present invention comprises applying tothe hair an aqueous system comprising one or more aqueous compositionswith a view toward reacting aminoethanethiol with a dihydroxybenzenetogether with an oxidizing agent selected from the group consisting ofpersulfates, ferricyanides and mixtures thereof, within a pH rangingfrom about 2 to about 11, preferably from about 5 to about 9. Theapplication to the hair is in such manner that sufficient oxidationtakes place within the hair shaft to provide a tinctorially effectiveamount of hair coloring pigments to permanently color the hair. Thesepigments are believed to be related to natural phaeomelanin andtrichochrome pigments, as hereinafter explained. It is believed thatintermediates to the melanin and melanin-like pigments obtained in theprocess diffuse into the hair shaft during the period of contact withthe formation of the pigment occurring in the hair shaft rather than onthe hair. As a result the hair is colored permanently and does not washout by repeated shampooing. The total time of the process during whichcomposition is applied and left in contact with the hair is normallyless than one hour, typically from about 5 to 50 minutes, preferably 5to 20 minutes.

"Hair dye composition" means an aqueous composition containing theaminoethanethiol and dihydroxybenzene reactants in tinctoriallyeffective concentrations to impart a coloration to the hair inaccordance with the process of the present invention. In the "one step"process described below the hair dye composition further contains anamount of the primary oxidizing agent to effect the quinone-formingreactions hereinafter described. In the "two step" process all or aportion of the primary oxidizing agent is provided in a separate aqueouscomposition for application to the hair following treatment of the hairwith the hair dye composition.

"Primary oxidizing agent" means the ferricyanide and persulfateoxidizing agents.

"Post-treatment composition" means an aqueous composition containing anoxidant optionally applied to the hair following the application of thehair dye composition in the one step process or following the secondstep oxidative treatment in the two-step process. The oxidant used inthe post-treatment step may be a primary oxidizing agent or may beanother oxidizing agent as indicated below.

By "permanent" is meant a color not removable by shampooing with aconventional surfactant-containing shampoo, the permanency beingattributable to the inability of the formed pigments to diffuse from thehair shaft in view of their molecular sizes.

By "applying" is meant contacting the hair to be dyed with the hair dyecomposition together with the primary oxidizing agent including anyoxidant contained in the post-treatment composition. Thus, the primaryoxidizing agent may be applied with the hair dye composition or as oneor more separate treatment compositions, in an amount sufficient toeffect a color change of the hair. The hair dye composition may beprepared just prior to contact with the hair or may be formed on thehair.

Trichochromes are yellow and red polycyclic pigments of defined chemicalstructure, several of which have been extracted from red hair andfeathers under alkaline conditions.

Phaeomelanins are reddish-brown nitrogen and sulfur containingmacromolecular pigments found in phaeomelanocytes. Phaeomelanins arederived from tyrosinase oxidation of tyrosine and subsequent reactionwith cysteine.

All percents by weight defined in this specification and claims arepercents by weight based on the total weight of the composition.

It is the object of this invention to provide a process and compositionthat leads to the formation phaeomelanin, trichochrome and relatedpigments. The reactions that are believed to take place are complex,with many of the reactions occurring outside the biosynthetic pathway.These reactions are believed to produce compounds analogous to thephaeomelanin and trichochrome pigments that are biosyntheticallyproduced, and are hereinafter referred to as phaeomelanin-like andtrichochrome-like pigments. Moreover, these definitions are intended toinclude any reaction products as may be formed by reaction of a directdye, primary intermediate or coupler with the dihydroxybenzenes orreaction intermediates thereof, under the oxidative conditions existingin the practice of the present invention. It is believed that theseterms and their meanings are well understood by the skilled artisan eventhough the exact chemical identity of some of the products, particularlythose formed by reaction of the intermediates formed during theoxidative process with a direct dye, primary intermediate and/or couplerin accordance with the present invention is not precisely known orunderstood.

Dihydroxybenzenes useful in the practice of the present invention arerepresented by Formulas I and II below: ##STR1## and theaminoethanethiols used herein are represented by the Formula III:##STR2## wherein ##STR3## R₂, R₃, R₄ and R₅, which may be the same ordifferent, are H, C₁ -C₆ alkyl or C₁ -C₆ hydroxyalkyl; R₁ is H or COOR₇; R₆ and R₇, which may be the same or different, are alkali metal, H orC₁ -C₆ alkyl, and n is 0 or 1.

The tinctorially effective amounts of the dihydroxybenzene andaminoethanethiol compounds depend upon many factors that can be readilyevaluated by the skilled artisan either from experience or from a fewtests. These factors include, for example, the color desired, theselected coloring agent or agents, the original color of the hair to betreated, the pH, auxiliary coloring agents employed, etc. Typically,however, the hair dye composition of the invention will contain fromabout 0.1 to 10% by weight of each of the dihydroxybenzene and theaminoethanethiol compounds, preferably 0.1 to 2%. When R_(d) is hydrogen(i.e. n=0) the aminoethanethiol and dihydroxybenzene components aregenerally present in the hair dye composition in approximately equimolaramounts, with a slight excess, typically not greater than about 15%, ofthe aminoethanethiol being present to account for side reactions. WhenR_(d) is CH₂ C(R₃)(NH₂)COOR₆ (i.e., n=1) the possibility exists forcompeting reactions leading to the formation of other chromophoriccompounds, e.g., indoles when the dihydroxybenzene is a catechol. It hasbeen found, however, that such reactions are suppressed by using a molarexcess of the aminoethanethiol component relative to thedihydroxybenzene. In such instance a mole ration of aminoethanethiol todihydroxybenzene of up to about 4:1 is acceptable, with a ratio of up to2:1 being preferred.

In some instances, however, it may be desirable to form suchchromophoric compounds (e.g., dihydroxyindoles and the resultingeumelanins), along with the pigments of the present invention. In suchinstances the molar ratio of the aminoethanethiol to thedihydroxybenzene may be as low as 1:2. Thus, the aminoethanethiol todihydroxybenzene mole ratio can vary from about 1:2 to 4:1, especiallyabout 1:1 to about 2:1. In some instances other reactants, e.g., acoupler, may react with the dihydroxybenzene reactants.

The preferred dihydroxybenzenes are dopa species, i.e., compounds ofFormula I in which n=1, as such compounds appear to most closely mimicthe biosynthetic melanin pathway. The dopa species are dopa, alpha alkyldopa having 1 to 4, preferably 1 to 2, carbons in the alkyl group, anddopa alkyl esters having 1 to 6, preferably 1 to 2, carbons in the alkylgroup. Dopa is especially preferred. When n=0, the preferred compoundsare catechols and paradihydroxybenzenes in which R₅ is H, C₁ to C₂ alkylor C₁ to C₂ hydroxyalkyl, with the catechols thereof being especiallypreferred, in particular 4-methylcatechol and hydroquinone. Of theaminoethanethiols, cysteine and aminoethanethiol are especiallypreferred.

The primary oxidizing agents employed in this invention may be selectedfrom persulfate and ferricyanide oxidizing agents, including ammoniumsalts and salts of alkali metals, preferably sodium or potassium. Thepresently preferred oxidizing agents are the easily soluble sodiumpersulfate and potassium ferricyanide salts. It is applicants' discoverythat the persulfate and ferricyanide oxidizing agents uniquely enablethe formation and subsequent reaction of intermediates leading to thephaeomelanin, phaeomelanin-like, trichochrome and trichochrome-likepigments of the present invention. Thus, applicants provide a hairdyeing process in which the dihydroxybenzene is first oxidized to form aquinone, the quinone then being substituted via a nucleophilic additionwith the aminoethanethiol, followed by further oxidation to thecorresponding thio-substituted quinone. This is followed by ring closureto form dihydrobenzothiazines. The ring closure reactions believed totake place after the initial substitution of the aminoethanethiol grouponto the phenyl nucleus are: ##STR4## Ring closure is followed byoxidative conversion of the resultant 1,4-dihydrobenzothiazines to thecoloring pigments of this invention. The proposed reaction sequence doesnot, however, preclude the possibility that more than oneaminoethanethiol substituent is added to the benzene ring and subsequentoxidation follows a different route. Accordingly, a slight molar excessof the aminoethanethiol, based on the substitution of only oneaminoethanethiol group, is normally employed.

It is seen that three oxidation steps take place in the sequence ofreactions leading to the formation of the hair dye pigments of thisinvention. The last oxidation step, namely, the conversion of thebenzothiazines to the pigments, may take place slowly using oxygen inthe air, but preferably will be accelerated by using an oxidant. Forthis conversion a variety of oxidants is suitable. Mention may be madeof the ferricyanide and persulfate primary oxidizing agents, as well aschlorite, periodate, iodate, permanganate, acidic nitrite, dichromateand other oxidants generally deemed useful in the hair dyeing art. A lowstrength hydrogen peroxide may also be used in a solution having a pH offrom about 7 to about 8.5. While useful, peroxide in high strength andat high pH is an excessively powerful oxidant, and may tend to bleachthe dyed hair. Of course, higher strength peroxide solutions are usefulas a post-treatment to lighten dyed hair. Generally, ferricyanide hasbeen found to be less useful as a post oxidant treatment.

In effecting the first two oxidations, namely, the quinone-formingreactions, the primary oxidizing agent is used. The amount of thisoxidizing agent for such purpose will generally be a stoichiometricallyequivalent amount. Since each quinone-forming reaction involves a twoelectron transfer and because ferricyanide can transfer only oneelectron, two moles ferricyanide are needed per mole of dihydroxybenzenefor each quinone-forming reaction, or a total of four molesferricyanide, which is its stoichiometrically equivalent amount. In thecase of persulfate, two electrons can be transferred. Accordingly, twomoles of persulfate are required per mole of dihydroxybenzene as itsstoichiometric equivalent amount. In view of the reaction kinetics,however, the primary oxidizing agent may be present in an excess overthe aforementioned theoretical amounts, especially in the case ofpersulfate. Typically, the amount of ferricyanide or persulfateoxidizing agent used in the practice of the process is less than a 50%excess over its respective stoichiometric equivalent amount.

The primary oxidizing agent is present in the hair dye composition or ina second step treatment composition in a concentration of from about 0.5to about 30% preferably from about 1 to about 15%, in the case ofpersulfate, and in a concentration of from about 0.5 to about 15%,preferably from about 1 to about 10%, in the case of ferricyanide. Thepersulfate and ferricyanide oxidizing agents may be used individually ormixed, or may be used in separate steps of the process.

Inasmuch as the pH of the reaction medium will vary during the reaction,it is desirable to provide a sufficient amount of a pH control agent inthe reaction medium to maintain the pH between about 2 to about 11,preferably from about 5 to about 9. In the process of the presentinvention, the preferred pH depends on the primary oxidizing agent usedand on the dyeing procedure (one-step dyeing or two-step dyeing). Thus,persulfates are usually optimal at alkaline pH, and ferricyanide is usedpreferably at a pH of 6 to 11, most preferably 7 to 9. The first step ofthe two step process if preferably conducted at high pH to maximizepenetration of the hair dye components into the hair.

Reagents for the control of pH in the compositions of this inventioninclude various conventional buffers including those based on inorganicsalts such as carbonates and bicarbonates, as well as aminic bufferssuch as TRIS. The pH control agents also include organic compoundswidely employed in hair colorant compositions to maintain the desiredpH. These include, for example, fatty acids, especially long chainmonocarboxylic or dicarboxylic acids such as dimer acid, linoleic acidor stearic acid, in combination with amines such as ammonia,2-amino-2-methyl propanol and monoethanolamine. Both types of reagentsare referred to herein and in the appended claims as pH control agents.

In the hair dyeing process of this invention the aminoethanethiol andthe dihydroxybenzene reactants are applied to the hair in an aqueoushair dye composition in the presence of the selected primary oxidizingagent, and are maintained in contact with the hair for a sufficientperiod of time for a tinctorially effective amount of pigment to form.The "contact" time as that term is employed herein is the period of timefrom the mixing of the reactants to the removal from the hair.

The pigment should form in the hair shaft so that it elicits a permanentcolor change. It is believed that the dihydroxybenzene andaminoethanethiol molecules and the intermediates formed in the course ofthe oxidative sequence are sufficiently small so that they will diffuseinto the hair strand along with the oxidizing agent and the aqueouscarrier. The trichochromes, phaeomelamins and analogous pigments thatform within the hair shaft, however, are such large molecules that theybecome trapped within the hair, thereby imparting permanency to thecolor. It will be apparent that applying the hair dye composition to thehair after an appreciable amount of oxidation has taken place is notsuitable since the pigments will form on the surface of the hair and notin the hair, and will be largely stripped away during subsequentshampooing.

The process of the present invention can be practiced in severalembodiments to achieve the desired results.

In the "one step" or "simultaneous" procedure, the aqueous hair dyecomposition comprises the aminoethanethiol and the aqueousdihydroxybenzene reactants as well as the primary oxidizing agent at therequisite pH. This hair dye composition is applied to the hair and ismaintained in contact with the hair to be treated until a tinctoriallyeffective amount of pigment is formed in the hair to effect the desiredresult. The oxidation of the benzothiazine intermediates to the pigmentsof the present invention may be accomplished slowly by using oxygen inthe air as the oxidizing agent or most preferably may be conducted bythe post- oxidation step hereafter described. The hair is then rinsedand dried.

When ferricyanide is the sole primary oxidizing agent in the one stepprocess, it is present in the hair dye composition in about astoichiometric equivalent amount, or in slight excess, usually not morethan 15%, over that amount, and it is usually desirable to conduct apost-treatment in which an oxidant different from the ferricyanideoxidizing agent is applied to the hair to effect conversion of thebenzothiazines to the pigments of the present invention. When persulfateis the sole primary oxidizing agent, excess of the persulfate over itsstoichiometric equivalent amount is preferably incorporated as set forthabove. Moreover, sufficient excess may be incorporated in the hair dyecomposition so as to satisfy the requirements of the benzothiazineoxidation. Alternately, the post-oxidative step may be used.

In the "two step" or "sequential process", the aqueous hair dyecomposition comprises the aminoethanethiol and the dihydroxybenzene,which composition is applied to the hair for a period of from about 1 toabout 30 minutes to permit these reactants to diffuse into the hairstrand. An aqueous solution containing the primary oxidizing agent isthen brought into contact with the hair for an additional 1 to 20minutes, preferably 2 to 10 minutes, until the desired coloration isattained. The hair is then rinsed and dried. The primary oxidizing agentis present in the aqueous solution at a concentration as previouslydescribed. The primary oxidizing agent stoichiometric requirements areanalogous to the one step process, and the benzothiazine intermediatesmay be converted to the pigments of the present invention via airoxidation, with an oxidative post-treatment composition, or usingprimary oxidizing agent present in excess in the aqueous solution. It isnoted that the primary oxidizing agent solution is different from theoxidative post-treatment composition because only the selected primaryoxidizing agents effect the formation of the quinones in amountssufficient to generate tinctorially effective pigment concentrations.

In a variation of this two step process, the hair dye compositioncomprises the aminoethanethiol and the dihydroxybenzene reactants alongwith a portion of the stoichiometric equivalent amount of the primaryoxidizing agent. This hair dye composition is applied to the hair and ismaintained in contact with the hair so that some oxidation takes place,with the reaction products diffusing into the hair strand along with theoriginal reactants. Oxidation of these reaction products as well asconversion of residual unreacted reactants will be completed in thesecond step. The primary oxidizing agent selected for the first step canbe the same or different in the second step.

In one embodiment of the two step process, ferricyanide is incorporatedin the hair dye composition in an amount of about one half of itsstoichiometric equivalent amount. Inasmuch as ferricyanide is especiallyreactive to the dihydroxybenzene, the conversion of the dihydroxybenzeneto the quinone followed by the nucleophilic addition of theaminoethanethiol is rapid and substantially complete. In the second steppersulfate is incorporated in the aqueous oxidizing agent solution in anamount of about one half of its stoichiometric equivalent amount plusthe desired excess as hereinbefore described. The second step completesthe conversion to the benzothiazine, and depending on the amount ofpersulfate in excess of the one half stoichiometric equivalent amount,will complete the oxidation to the pigments. The concentrations of theprimary oxidizing agents in the hair dye composition and the oxidizingagent solution are the same as set forth above. Of course, the amount ofprimary oxidizing agent can be proportioned between the hair dyecomposition and the oxidizing agent solution as desired, providedsufficient oxidizing agent is used to effect the formation of thequinones.

As indicated above, the hair treated in the one step or the two stepprocesses may be subjected to a post-treatment with an oxidant solution.This post-treatment composition is usually employed following the onestep procedure, especially when the primary oxidizing agent used in theone step procedure is a ferricyanide. The purpose of the oxidativepost-treatment is to complete the conversion of the various intermediatechemical species present in the aqueous reaction medium at this stage inthe process including especially the benzothiazines as well as otherimmediate melanin precursors to the pigments of the present invention.The degree to which completion is required depends upon the amount ofprimary oxidizing agent in excess of the stoichiometric equivalentamount used in the practice of the one step or the two step processes,as described above. Thus, the oxidative post-treatment can be used toeffect essentially all of the conversion of the benzothiazines topigments, or may be used to merely complete the conversion of residualpigment precursors into the useful pigments of this invention. In thisregard it should be understood that the phaeomelanin, trichochrome andanalogous pigments obtained by the process of the present invention arethe dimer, trimer and higher oligomer reactive products obtained frombenzothiazine. It is believed that the benefit of the oxidativepost-treatment lies in assisting in the conversion to the more highlycolored and higher molecular weight pigment species, resulting in deepercolors. Generally, the oxidative post-treatment composition is appliedto the hair following a rinse after completion of the one step or twostep process.

As previously indicated, any conventional oxidizing agent generally usedin oxidative hair dye processes can be employed as the oxidant in theoxidative post-treatment procedure. Suitable oxidants for this step are,for example, the alkali metal and ammonium salts of ferricyanides,persulfates, perborates, iodates, periodates, permanganates,dichromates, acidic nitrites, dilute hydrogen peroxide, chlorites, andcompatible mixtures thereof. Persulfates and periodates are preferred.Periodates are especially preferred. Ferricyanides are not preferred.

The oxidant solution used in the oxidative post-treatment typicallycontains from about 0.1 to about 30% by weight oxidant, and is appliedto the hair in sufficient amount to ensure high yield of the pigments.The solution is generally provided in substantial excess, and ispermitted to remain in contact with the hair for about 1 to 30 minutes,preferably 2 to 15 minutes. The pH of the solution is typically fromabout 4 to about 10, preferably from about 6 to about 9.

A further aspect of the present invention is the optional incorporationof a hair color modifier selected from the group consisting of directdye, primary intermediate or coupler, and mixtures thereof in thereaction mixture. It is believed these components when present in thereaction mixture react at least in part with the intermediate compoundsformed during the sequence of reactions leading to pigment production,thereby providing trichochrome-like and phaeomelanin-like compounds thatimpart additional chromatic characteristics to the pigments ultimatelyobtained. When such oxidizable color modifying compounds are employed,the amount of primary oxidizing agent in the reaction mixture isincreased to provide for the oxidation of these materials since some ofthem will be directly oxidized in the usual way rather than reactingwith an intermediate of the primary reaction sequence. It will beapparent to the skilled artisan that by use of these auxiliary coloringagents, a wide variety of tints, tones and shades can be achieved. Aspreviously mentioned, the dopa species may under certain circumstancesbe considered to be color modifiers, in that oxidation to adihydroxyindole can take place when sufficient primary oxidizing agentis present coupled with a deficit of the aminoethanethiol. Thedihydroxyindoles are useful as they provide eumelanins, and can providedesired shades to the final hair color.

The concentration of hair color modifiers is normally less than about 10mg/ml, and preferably is present in the reaction medium at from about0.01 to about 5 mg/ml, most preferably from about 0.05 to about 2 mg/ml.The amount of these components should not be so great as to prevent theformation of the principal pigment. That is, the process of the presentinvention contemplates reaction of only a portion of the intermediatereaction products with the hair color modifiers.

A wide variety of direct dyes, primary intermediates and couplers areknown to the skilled artisan and can be employed in this invention.

The presently preferred primary intermediates and couplers include:

    ______________________________________                                        Primary   p-phenylenediamine                                                  Intermediates:                                                                          p-aminophenol                                                                 o-aminophenol                                                                 N,N-bis(2-hydroxyethyl)-p-phenylenediamine                                    2,5-diaminopyridine                                                           p-toluenediamine                                                    Couplers: resorcinol                                                                    m-aminophenol                                                                 1-naphthol                                                                    5-amino-o-cresol                                                              2-methylresorcinol                                                            N-acetyl dopa                                                                 4,6-di(hydroxyethoxy)-m-phenylenediamine                                      m-phenylenediamine                                                  ______________________________________                                    

Direct dyes which may be used in the invention include, for example,nitro dyes, azo dyes and anthraquinone dyes.

The variously described embodiments of the present invention may alsoinclude in the hair dye composition or in any of the oxidizingagent-containing solutions including the post-treatment solution one ormore optional ingredients. Such ingredients include well-knownconventional additives usually employed in oxidative hair coloringcompositions such as organic solvents, thickeners, surface-active agentsto enhance diffusion of the dyeing agents into the hair shaft, pHadjusting agents, antioxidants, fragrances and chelating agents.

Surface-active agents employed in the dyeing compositions of thisinvention can be anionic, nonionic, cationic, amphoteric orzwitterionic. By way of examples of the various types of surface-activeagents, there can be mentioned: higher alkylbenzene sulfonates;alkylnaphthalenesulfonates; sulfonated esters of alcohols and polybasicacids; taurates; fatty alcohol sulfates; sulfates of branched chain orsecondary alcohols; alkyldimethylbenzylammonium chlorides; salts offatty acids or fatty acid mixtures; N-oxyalkylated fatty acidalkanolamides, and the like. Illustrative of specific surfactants therecan be mentioned: sodium lauryl sulfate; polyoxyethylene lauryl ester;myristyl sulfate; glycerol monostearate; triethanolamine oleate; sodiumsalt of palmitic methyl taurine; cetyl pyridinium chloride; laurylsulfonate; myristyl sulfonate; lauric diethanolamide; polyoxyethylenestearate; ethoxylated oleyl diethanolamide; polyethylene glycol amidesof hydrogenated tallow; stearyldimetnyi benzyl ammonium chloride;dodecylbenzene sodium sulfonate; triethanolamine salt ofp-dodecylbenzene sulfonate; nonylnaphthalene sodium sulfonate; dioctylsodium sulfonsuccinate; sodium N-methyl-N-oleyl taurate; oleic acidester of sodium isethionate; sodium dodecyl sulfate; the sodium salt of3-diethyl tridecanol-6-sulfate and the like. The quantity ofsurface-active agent can vary over a wide range, such as from about0.05% to 15% and preferably from about 0.10 to 5% by weight of thecomposition, The anionic and nonionic surfactants are employed typicallyas emulsifiers, while the cationic surfactants are useful to impart ahair conditioning benefit to the hair. Care must be exercised whenanionic and cationic surfactants are both incorporated, in view ofpossible incompatibility.

Chelating and sequestering agents include, for example,ethylenediaminetetraacetic acid, sodium citrate, etc., and may bepresent in an amount of under about 1%.

A thickening agent may also be incorporated in the dyeing composition ofthis invention, which may be one or several of those commonly used inhair dyeing. These are exemplified by such products as sodium alginate,gum arabic, cellulose derivatives such as methylcellulose (e.g.,Methocel 60HG), the sodium salt of carboxymethylcellulose,hydroxyethyl-cellulose (e.g., Cellosize QP-40), acrylic polymers such aspolyacrylic acid sodium salt, and inorganic thickeners such asbentonite. The quantity of the thickening agent can also vary over awide range, even as high as 20%. Ordinarily it will range from about 0.1to 5% by weight of the composition. The viscosity of the composition mayvary from about 1 cp to about 100,00 cps. For a typical lotionformulation, composition viscosity is between about 100 cps to about10,000 cps, at which viscosity the composition can be applied to thehair without running or dripping.

The list of optional ingredients is not intended as limiting. Othersuitable adjuvants for inclusion in the hair dye composition or in theoxidant solutions are recited, for example, in Zviak, The Science ofHair Care (1986) and Balsam and Sagarin, Cosmetics: Science andTechnology, Vol. 2 (Second Edition 1972).

The process of the present invention may conveniently be practiced byproviding premeasured amounts of the reactants in separate containerspackaged in kit form. The user simply admixes the reactants forapplication to the hair in accordance with the selected practice of theinvention. It will be apparent that no special expertise is required tocarry out the process, and accordingly the product and process areequally suitable for in-home use by the nonprofessional as well as salonuse by the professional. Advantageously, the product in kit form isshelf-stable and is therefore suitable for retail sale and withoutprecautions required for some hair colorant compositions, e.g., storageunder anaerobic conditions.

The kit provided in accordance with this aspect of the inventioncomprises hair colorant precursor, a first container containing theoxidizable colorant mixture and a second container containing theoxidant. The buffer may be individually packaged in a third container ormay be present in the first or second container. Selected modifiers maybe mixed with the basic hair colorant of the invention or may be in aseparate container. Of course, the dihydroxybenzene and theaminoethanethiol may be in separate containers, but it is presentlypreferred that they be in the same container.

While the kit may include packets containing amounts, preferablypremeasured, of dry powders for preparation of these solutions, it ismore convenient to provide them as solutions. Moreover, solutionscontaining premeasured quantities of the constituents facilitates theircorrect use by the consumer.

One or more additional containers containing the optional constituentsmay be provided in the kit. The optional constituents may also becontained within the solutions of the previously described containers,barring any incompatibility.

The consumer admixes the components of the kit, suitably as the aqueoussolutions or as dry powders and water, according to writteninstructions, to obtain the aqueous compositions for application to thehair. Mixing may be conducted in a separate vessel supplied with orexternal to the kit, or may take place in a container of the kit adaptedto provide sufficient head space for mixing. The reactants may also beadmixed on the hair of the user. Reaction commences upon combining theoxidizing agent with the dehydroxybenzene and aminoethanethiolreactants. The hair dye component will subsequently oxidize as describedherein whereby a permanent hair color is obtained. After the desiredhair shade is reached, most preferably within about 30 minutes, the hairdye composition that was applied to the hair is removed, preferably witha conventional shampoo.

In the examples which follow, the hair coloring effects achieved withthe process of this invention are evaluated utilizing the standardHunter Tristimulus values. In the Hunter method, the parameters a and bmay be positive or negative and define the chromatic condition of thehair. Thus, the more positive the a value, the greater the redness ofthe hair, while a negative a value indicates greenness. Similarly,positive b values indicate yellowness, while negative b values indicateblueness. The L parameter is a measure of color intensity, and has avalue of 0 for absolute black to 100 for absolute white. Generally, hairhaving an L value of about 15 or less is considered black, while an Lvalue of about 60 is white. It should be understood that the L valuescale is not linear, but rather is sigmoidal. Proximate to 0 andproximate to 100 hair color intensity apparent to the human eye variesminimally with unit changes in the L value. Between values of about 20to about 50, hair color intensity varies significantly with unit changesin L value. Thus, the Hunter values are more sensitive in the regionwhere the human eye is able to perceive color changes.

EXAMPLE 1

100 mg DOPA (0.5 mmole) and 61 mg cysteine (0.5 mmole) were dissolved in10 ml of an aqueous solution of TRIS buffer (850 mg TRIS; 3.5 ml 1N HClin 10 ml). 228 mg ammonium persulfate (1.0 mmole) were added anddissolved as fast as possible (by shaking). The solution (pH approx.8.2) was applied to a tress of white hair and left for 20 minutes. Thehair was briefly rinsed with water, shampooed and dried. Huntermeasurements were made on the dyed hair and compared to the undyed hairas noted below:

    ______________________________________                                                  L          a      b                                                 ______________________________________                                        untreated hair:                                                                           62.6         0.2    18.3                                          treated hair:                                                                             41.5         -0.9   8.3                                           ______________________________________                                    

EXAMPLE 2

A tress of white hair was treated as in Example 1. After rinsing withwater, the tress was exposed to an aqueous formulation, containingapprox. 10% (NH₄)₂ S₂ O₈ for 4 minutes. Afterwards, the tress was rinsedwith water, shampooed and dried. The Hunter values were:

    ______________________________________                                                  L          a      b                                                 ______________________________________                                        untreated hair:                                                                           62.6         0.2    18.3                                          treated hair:                                                                             29.2         3.7    10.9                                          ______________________________________                                    

EXAMPLE 3

100 mg DOPA (0.5 mmole) and 121 mg cysteine (1.0 mmole) were dissolvedin 10 ml of an aqueous solution of TRIS buffer (640 mg TRIS; 2.6 ml 1NHCl in 10 ml). 342 mg ammonium persulfate (1.5 mmole) were added anddissolved as fast as possible (by shaking). The solution (pH approx.8.0) was applied to a tress of white hair and left for 20 minutes. Thehair was briefly rinsed with water, shampooed and dried. The Huntervalues were:

    ______________________________________                                                  L          a      b                                                 ______________________________________                                        untreated hair:                                                                           62.6         0.2    18.3                                          treated hair:                                                                             38.4         -0.9   6.7                                           ______________________________________                                    

EXAMPLE 4

100 mg DOPA (0.5 mmole) and 61 mg cysteine (0.5 mmole) were dissolved in10 ml of an aqueous solution of TRIS buffer (640 mg TRIS; 2.6 ml 1N HClin 10 ml). 659 mg potassium ferricyanide (2.0 mmole) were added anddissolved as fast as possible (by shaking). The solution (pH approx.7.5) was applied to a tress of white hair and left for 20 minutes. Afterrinsing with water, the tress was exposed to an aqueous formulationcontaining approx. 10% (NH₄)₂ S₂ O₈ for 4 minutes. Afterwards, the tresswas rinsed with water, shampooed and dried. The Hunter values were:

    ______________________________________                                                  L          a      b                                                 ______________________________________                                        untreated hair:                                                                           62.6         0.2    18.3                                          treated hair:                                                                             14.5         0.6    1.3                                           ______________________________________                                    

EXAMPLE 5

100 mg DOPA (0.5 mmole) and 121 mg cysteine (1.0 mmole) were dissolvedin 10 ml of an aqueous solution of TRIS buffer (640 mg TRIS; 2.6 ml 1NHCl in 10 ml). 659 mg potassium ferricyanide (2.0 mmole) were added anddissolved as fast as possible (by shaking). The solution (pH approx.7.5) was applied to a tress of white hair and left for 20 minutes. Afterrinsing with water, the tress was exposed to an aqueous formulation,containing approx. 10% (NH₄)₂ S₂ O₈ for 4 minutes. Afterwards, the tresswas rinsed with water, shampooed and dried. The Hunter values were:

    ______________________________________                                                  L          a      b                                                 ______________________________________                                        untreated hair:                                                                           62.6         0.2    18.3                                          treated hair:                                                                             27.3         2.4    9.4                                           ______________________________________                                    

What is claimed is:
 1. A method of permanently coloring hair to adesired color comprising the steps of:(a) applying an aqueous system tothe hair at a pH of from abut 2 to 11, the aqueous system comprising atinctorially effective amount of (i) a dihydroxybenzene having astructure: ##STR5## (ii) an aminoethanethiol having the formula ##STR6##and (iii) a ferricyanide oxidizing agent, wherein ##STR7## R₁ is H orCOOR_(7;) R₂, R₃, R₄ and R₅, which may be the same or different, are H,C₁ -C₆ alkyl or C₁ -C₆ hydroxyalkyl; R₆ and R₇, which may be the same ordifferent, are alkali metal, H or C₁ -C₆ alkyl, and n is 1, theferricyanide oxidizing agent being present in said aqueous system in atleast about a stoichiometric equivalent amount relative to thedihydroxbenzene component (i), and (b) permanently coloring the hair byallowing the aqueous system to remain in contact with the hair for aperiod of time sufficient to achieve the desired color.
 2. The method ofclaim 1 wherein the aqueous system comprises an aqueous hair dyecomposition containing the dihydroxybenzene and the aminoethanethiolhair dye components, each of which is present at a concentration of fromabout 0.1 to about 10% by weight of the hair dye composition.
 3. Themethod of claim 2 wherein the hair dye composition further contains theferricyanide oxidizing agent, said oxidizing agent being present in thehair dye composition at a concentration of from about 0.1 to 15%, theoxidizing agent being present in the hair dye composition in saidstoichiometric equivalent amount.
 4. The method of claim 3 wherein theferricyanide oxidizing agent is potassium ferricyanide present in thehair dye composition in an amount that is less than about a 15% excessover its stoichiometric equivalent amount.
 5. The method of claim 2wherein the aqueous system further comprises an aqueous solutioncontaining at least a portion of the ferricyanide oxidizing agentpresent in the system, said aqueous solution being applied to the hairfollowing the application of the hair dye composition to the hair. 6.The method of claim 5 wherein the ferricyanide oxidizing agent ispresent in the aqueous system in an amount of from about astoichiometric equivalent amount to about a 50% excess over such amount.7. The method of claim 6 wherein the portion of the ferricyanideoxidizing agent not contained in the aqueous solution is present in thehair dye composition.
 8. The method of claim 1, 3, or 6 wherein the moleratio of the aminoethanethiol to the dihydroxybenzene is from about 1:2to about 4:1.
 9. The method of claim 8 wherein the mole ratio is about1:1 to about 2:1.
 10. The method of claim 8 wherein n=1; R₁ is H orCOOH; R₂ and R₃ are each H; R₄ and R₅ are each H or C₁ -C₄ alkyl; and R₆is H or C₁ -C₂ alkyl.
 11. The method of claim 10 wherein thedihydroxybenzene has the structure of formula I.
 12. The method of claim11 wherein R₁ is COOH, and R₄, R₅ and R₆ are each H.
 13. The method ofclaim 1, 3, 5 or 7 further comprising the step of:(c) applying to thehair following application of the aqueous system to the hair an aqueouspost-treatment composition containing an oxidant.
 14. The method ofclaim 13 wherein the post-treatment oxidant is selected from the groupconsisting of periodate, iodate, chlorite, acidic nitrite and persulfatesalts, the oxidant being present at a concentration of from about 0.1 toabout 30% by weight of the post-treatment composition.
 15. The method ofclaim 14 wherein the oxidant is selected from the group of sodiumpersulfate and sodium periodate.
 16. The method of claim 1, 3, or 6wherein the aqueous system further comprises a color modifier selectedfrom the group consisting of direct dyes, primary intermediates,couplers and mixtures thereof.
 17. An aqueous hair dyeing system forpermanently dyeing hair comprising tinctorially effective amounts of (a)a dihydroxybenzene having a structure: ##STR8## (b) an aminoethanethiolhaving the formula ##STR9## (c) a ferricyanide oxidizing agent, wherein##STR10## R₁ is H or COOR_(7;) R₂, R₃, R₄ and R₅, which may be the sameor different, are H, C₁ -C₆ alkyl or C₁ -C₆ hydroxyalkyl; R₆ and R₇,which may be the same or different, are alkali metal, H or C₁ -C₆ alkyl,and n is 1, said system having a pH of from abut 2 to about 11 , theferricyanide oxidizing agent being present in the system in at leastabout a stoichiometric equivalent amount relative to thedihydroxybenzene component (a).
 18. The system of claim 17 wherein thedihydroxybenzene (a) and aminoethonthiol (b) are present in a hair dyecomposition, each such component being present at a concentration offrom about 0.1 to about 10%, the mole ratio of the component (a) to thecomponent (b) being from about 2:1 to about 1:4.
 19. The system of claim18 wherein the ferricyanide oxidizing agent is contained in the hair dyecomposition at a concentration of from about 0.1 to 15%.
 20. The systemof claim 19 wherein the ferricyanide oxidizing agent is contained in thehair dye composition in an amount of from about a stoichiometricequivalent amount to about a 50% excess over such amount.
 21. The systemof claim 18 wherein the ferricyanide oxidizing agent is contained in anaqueous solution having a concentration of from about 0.1 to 15%. 22.The system of claim 21 wherein the ferricyanide oxidizing agent iscontained in the aqueous solution in an amount of from about astoichiometric equivalent amount to about a 50% excess over such amount.23. The system of claim 18 wherein the hair dye composition contains aportion of the ferricyanide oxidizing agent and wherein the remainder ispresent in an aqueous solution.
 24. The system of claim 23 wherein thehair dye composition contains about one-half of the stoichiometricequivalent amount of the ferricyanide oxidizing agent and the aqueoussolution contains the ferricyanide oxidizing agent in an amount of fromabout one-half of the stoichiometric equivalent amount to about a 50%excess over the total stoichiometric equivalent amount, theconcentration of the ferricyanide oxidizing agent in each of the hairdye composition and the aqueous solution being from about 0.1 to about15% by weight.
 25. The system of claim 20, 22 or 24 wherein the moleratio of dihydroxybenzene (a) to aminoethanethiol (b) is from about 1:1to about 1:2.
 26. The system of claim 20, 22 or 24 wherein the pH of thehair dye composition is from about 5 to about
 9. 27. The system of claim22 or 24 wherein the pH of the aqueous solution is from about 5 to about9.
 28. The system of claim 17, 19, 21 or 23 further comprising anaqueous post-treatment composition containing a post-treatment oxidant.29. The system of claim 28 wherein the post-treatment oxidant isselected from the group consisting of persulfate, periodate, iodate,chlorite and acidic nitrite salts, the oxidant being present at aconcentration of from about 0.1 to about 30% by weight of thepost-treatment composition.
 30. The system of claim 29 wherein theoxidant is sodium persulfate or sodium periodate.
 31. The system ofclaim 17 wherein n=1; R₁ is H or COOH; R₂ and R₃ are each H; R₄ and R₅are each H or C₁ -C₄ alkyl, and R₆ is H or C₁ -C₂ alkyl.
 32. The systemof claim 31 wherein the dihydroxybenzene has the structure of formula I.33. The system of claim 33 wherein R, is COOH, and R₄, R₅ and R₆ areeach H.
 34. The composition of claim 17 further comprising a colormodifier selected from the group consisting of direct dyes, primaryintermediates, couplers, and mixtures thereof.
 35. A hair dyeing kit forpermanently dyeing hair having in a single package a plurality ofcontainers, the kit comprising (a) a first container containing anaqueous hair dye composition comprising (i) about 0.1 to 10%dihydroxybenzene having a structure: ##STR11## and (ii) about 0.1 to 10%of an aminoethanethiol having the formula ##STR12## wherein ##STR13## R₁is H or COOR₇ ; R₂, R₃, R₄ and R₅, which may be the same or different,are H, C₁ -C₆ alkyl or C₁ -C₆ hydroxyalkyl; R₆ and R₇, which may be thesame or different, are alkali metal, H or C₁ -C₆ alkyl, and n is 1, and(b) a second container containing an aqueous solution comprising aferricyanide oxidizing agent, a pH control agent being present in anyone of said first or said second containers or in a third container, theamount of said pH control agent contained in the kit being sufficient toprovide a pH of from abut 2 to 11 when the contents of the first andsecond containers or of the first, second and third containers arecombined to form an aqueous hair dye system and the amounts of theaminoethanethiol, the dihydroxybenzene and ferricyanide oxidizing agentin the kit being sufficient to effect a permanent dyeing of hair whenthe contents of the containers are combined to form of the aqueous hairdye system and applied to the hair, the ferricyanide oxidizing agentbeing present in the system in at least about a stoichometric equivalentamount relative to the dihydroxybenzene component (i).
 36. The hairdyeing kit of claim 35 further comprising, in a container other than thecontainer containing the ferricyanide oxidizing agent, a color modifierselected from the group consisting of direct dyes, ferricyanideintermediates, couplers, and mixtures thereof.
 37. The hair dyeing kitof claim 35 wherein the pH of the aqueous system is maintained betweenabout 5 to about
 9. 38. The hair dyeing kit of claim 35 furthercomprising a container of an aqueous composition comprising apost-treatment oxidant.